(1) Field of the Invention
The present invention relates generally to video displays and their associated driving circuits and in particular to LCD video display column driving circuits that use a simplified multiplexing arrangement for data lines and pixel capacitors that are precharged to a selected voltage level prior to the application of video data signals to enable selected ones of the data lines and pixel capacitors to be additionally charged or discharged to an appropriate level by the incoming video data signals to enhance the operation of the display.
(2) Description of Related Art
Matrix display devices commonly utilize a plurality of display elements that are arranged in a matrix of rows and columns and supported on opposing sides of a thin layer of electro-optic material. Switching devices are associated with the display elements to control the application of data signals thereto. The display elements include a pixel capacitor driven by a transistor as a switching device. One of the pixel electrodes is on one side of the matrix display and a common electrode for each of the pixels is formed on the opposite of the matrix display. The transistor is usually a thin-film transistor (TFT) that is deposited on a transparent substrate such as glass. The switching transistor has its source electrode connected to the pixel electrode that is deposited on the glass on the same side of the display matrix as the switching transistor. The drain electrodes of all of the switching transistors in a given column are connected to the same column conductor to which data signals are applied. The gate electrodes of all of the switching transistors in a given row are connected to a common row conductor to which row selection signals are applied to switch all the transistors in a selected row to the ON condition or state. By scanning the row conductors with the row selection signals, all of the switching transistors in a given row are turned ON and all of the rows are selected in a sequential fashion. At the same time, video data signals are applied to the column conductors in synchronism with the selection of each row. When the switching transistors in a given row are selected by the row select signal, the video data signals supplied to the switching transistor electrodes cause the pixel capacitors to be charged to a value corresponding to the data signal on the column conductor. Thus each pixel with its electrodes on opposite sides of the display acts as a capacitor. When the signal for a selected row is removed, the charge in the pixel capacitor is stored until the next repetition when that row is again selected with a row select signal and new voltages are stored therein. Thus a picture is formed on the matrix display by the charges stored in the pixel capacitors.
It is also known to precharge the pixel capacitors of the presently selected row to a predetermined voltage level prior to the video data signals being applied to the column conductors as set forth in commonly assigned copending application Ser. No. 971,721, filed Nov. 3, 1992. By doing so, the pixel capacitor can then be additionally charged or discharged to the level of the succeeding video data in a shorter time period than required if the pixel capacitor was charged only by the video data signals. To accomplish the precharging function, precharging TFTs are deposited onto the glass substrate with each of the drain electrodes connected to a column conductor and each of the gate electrodes connected together and to a precharge circuit and each of the source electrodes connected to a predetermined voltage source.
Then prior to the video data signals being applied, the precharge circuit turns ON each of the precharging TFTs thereby allowing the voltage source to charge the pixel capacitors to a predetermined level.
It is to be understood that the use of the term "video" herein, although it has been generally applied to the use of signals for television, is intended to cover displays other than TV pictures or displays. Such displays may be hand-held games having an LCD display with moving figures thereon and the like.